1. Field of the Invention
This invention relates to an optical lens system for an instrument and more particularly relates to a lens relay which forms part of a lens relay system having a plurality of lens relays for a medical endoscope and wherein the medical endoscope is capable of withstanding an autoclaving process of sterilization in a medical environment.
2. Description of the Prior Art
The use of rod-type lens elements or elongated lens elements in an endoscope is well known. One well known lens relay system is described in U.S. Pat. No. 3,257,902 and is referred to as the "Hopkins" relay lens system. The "Hopkins" relay lens system transfers an optical image developed by an objective lens to an adjacent relay lens system or an eyepiece lens and achieves an acceptable level of transfer of a high brightness image with correction of optical aberrations. The "Hopkins" relay lens system uses a combination of bi-convex rod-type lens and meniscus lens. A typical "Hopkins" relay lens system has two cemented or bonded gaps per relay lens. A medical endoscope uses a plurality of "Hopkins" relay lens system. Therefore, there can be as many as 13 cemented or bonded gaps per endoscope.
U.S. Pat. No. 5,005,960 discloses a relay lens system having four optical elements in symmetrical arrangement. In the relay lens system of U.S. Pat. No. 5,005,960, two rod type lens elements and two convex/concave optical elements are used with one rod system lens and one further lens, all of which are bonded to each other. Thus two cemented or bonded gaps are required for each relay lens.
Another known endoscope relay is disclosed in U.S. Pat. No. 5,059,009. The relay lens disclosed in U.S. Pat. No. 5,059,009 includes two identical end lenses affixed to opposed ends of a center lens to define a cylinder. The relay lens is symmetrical about a plane bisecting the center of the center lens. The axial length of each end lenses is equal to or greater than one-half its diameter. Each end lens has one end connected to the center lens. Thus, each relay lens has two cemented gaps or four adhesive-glass surfaces for each relay lens.